Field of the Invention
This invention relates to a process for producing optical members.
Most of optical members such as lens, mirror, filter and the like, are formed of glass.
Glass has various kinds, and glass optical members of various characteristics can be produced depending on demand, and further, optical surfaces such as plane and spherical surfaces can be formed with a high precision by grinding. However, grinding takes a long time and the processing cost is disadvantageously high. In addition, in the case of production of aspherical optical elements, the processing cost becomes much higher.
Other process for producing optical members capable of solving these drawbacks is a process of shaping a transparent resin by pouring a resin into a mold, so-called, a process for fabricating a plastic lens. According to this process, a grinding processing is not necessary, and when appropriate conditions are selected, the plastic optical members can be fabricated at a low cost by mass production. However, it is not easy to produce optical members having high optical precision, and the plastic materials are poorer than glass materials with respect to physical and chemical properties, and have particularly drawbacks that coefficient of thermal expansion and change of refractive index due to heat are large, and strain and formation of recess are internally formed upon processing.
As a method for complementing the drawbacks of glass materials and resin materials, there is a method of producing an optical member composed of both plastic material and glass material. This method comprises disposing near a glass substrate and a master having an optical surface of an optical member to be formed, sandwiching a resin therebetween or pouring a resin therebetween, solidifying the resin to form a resin layer between the glass substrate and the master, and separating the glass substrate from the master resulting in the production of an optical member constituted of a glass substrate and a resin layer.
According to this method, it is necessary to grind precisely the glass substrate to some extent, but an optical precision as an optical member can be obtained by the resin layer so that the grinding of the glass itself can be reduced to a great extent. Moreover, since the resin layer is a thin film, the resin layer is affected only little by thermal expansion and change in refractive index and the formation of strain and formation of recess can be suppressed to the minimum.
Optical members having an aspherical surface such as aspherical lenses can be also easily produced in a way similar to the production of optical members having a spherical surface by rendering the shape of the master aspheric. One of the biggest problems of the method using a master is that, after forming a resin layer between a master and a glass substrate, it is not easy to separate the glass substrate from the master without damaging the optical surface of the resin layer. In order to avoid such damage, a material preventing adhesion with a master and enabling the releasing easy has been incorporated in the resin material. Example of such material are silicone oil, various waxes and the like. In many cases, these materials are not or less compatible with the resin materials so that the materials ooze to the surface of the resin layer resulting in releasing. Therefore, the materials often deteriorate mechanical characteristics, transparency, surface physical properties and the like. Further, when a secondary processing such as adhering other optical members is applied to the surface of the resin layer, the material disadvantageously lowers adhesion of the adhesives.
Alternatively, it is generally used that a releasing agent is not mixed with the resin material, but applied to the surface of a master to form a releasing layer to prevent the adhesion between a resin material and a master.
As materials for such releasing layer, there may be used silicone oil, silicone grease, silicone varnish, carnauba wax, mineral wax, fluorine-containing resin powder or coating film, water-soluble resins, glycerine, various oils and fats, stearic acid salts, and the like. However, these releasing agents have not given a sufficient releasing effect. In particular, in the case of precision molding of optical members such as lens, mirror and the like, liquid monomers or oligomers for acrylic resins, expoxy resins and the like are often used as the shaping material, and when the conventional releasing agents are used, adhesion of the poured liquid material with a master often occurs, in particular, a material of excellent adhesion such as epoxy resin is liable to adhere to a master.
Molding precision at the surface of resin layer is very important for optical members, and therefore, it is desired that a releasing agent is thin as far as possible, but when conventional releasing agents are used, it is not possible to obtain a thin resin layer and when a resin layer is made thin, the releasing layer is often partly peeled off.
In order to avoid such difficulty as above, heretofore, an metallic vapor deposition film such as gold, silver, copper and the like has been used as a releasing layer. The releasing layer may be formed by depositing an extremely thin film of the metal on the surface of a master according to sputtering, vacuum vapor deposition, and the like. On the resulting thin metal film was molded a desired resin material by means of casting, and then releasing is effected. The metallic deposited layer for releasing is taken out in such a form that the metallic deposited layer is attached to the surface of the shaped article. Therefore, at the next stage the metal layer as a releasing layer should be removed. This removing may be carried out by chemically dissolving with acid or alkali, or a mechanical means such as peeling off with an adhesive tape and the like. As a result, the surface of the shaped article is affected by chemicals to cause surface roughness and surface defects and further, a step for removing a releasing layer is disadvantageously necessary.